The invention relates to that aspect of ophthalmic surgery which is concerned with laser operations upon the external surface of the cornea, such operations involving controlled ablation of the cornea with penetration into the stroma and volumetric removal of corneal tissue whereby said external surface is characterized by a sculptured new curvature having improved optical properties.
Several different techniques and related apparatus are described for such sculpture of the cornea, in pending L'Esperance patent applications, including Ser. No. 748,358, (now U.S. Pat. No. 4,665,913) Ser. No. 691,923, (now U.S. Pat. No. 4,669,466) Ser. No. 891,169, and Ser. No. 891,285, (now U.S. Pat. No. 4,732,148) and reference is made to these patent applications for greater detail. Suffice it to say that these techniques rely on ultraviolet radiation which is preferably of less than 200-nm wavelength, as is provided by an excimer laser operating with argon fluoride Typical beam dimensions of the excimer laser are rectangular, and said Ser. No. 891,169 discloses a circular opening in a mask for reducing the laser beam to a cylinder of circular section; thereafter, the cylindrical beam is variously characterized so that at incidence with the cornea and on the eye axis, the distribution of laser-flux density will be a correspondingly distributed pattern of cornea-curvature correction.
In said Ser. No. 891,285, the sculpturing result for cornea-curvature correction is achieved by exposing the cornea to a sequence of mask openings, of different but related areas, whereby the cumulative effect is to so expose certain areas more in relation to others that the consequence is the desired net curvature change.
The techniques of both said applications Ser. No. 891,169 and Ser. No. 891,285 involve non-scanning use of the involved laser beam, and they assume that a sufficiently homogenous beam will be available prior to characterizing the same for sculpturing delivery to the cornea. But we have found that the flux-density distribution within such a beam is not necessarily uniform and that it can vary with time, thus presenting the possibility of impaired quality of the intended curvature correction. The present invention addresses this specific problem.